Today marks the day that Microsoft Vista goes on sale to consumers worldwide.

The business versions have been out for a couple of months, and now four home versions have joined them.

Analysts are estimating that the home versions will be installed on more than 100m computers across the world within a year.

The New York launch of the software saw performers abseiling down a skyscraper decorated in Microsoft's colours and rock bands lighting up the Nokia Theatre.

The UK's launch was held at the British Library with not quite so much fanfare.

The operating system has caused concern to security firms who claim that Microsoft is locking them out of the system and making it difficult for them to protect it.

In addition, there is now some controversy over Vista's pricing, which is nearly double in the UK. In the US, prices start at $100 (£52) for Home Basic and go up to $249 (£127) for Ultimate; in the UK, the same software is priced at £100 and £250, respectively.

The software is also quite power hungry, and demands higher than average specs in order to run. Minimum system requirements are 512MB of RAM, an 800Mhz processor, and 15GB of free hard disk space.

Some countries, however, will receive Vista Starter, a “lite” package designed for developing nations where computer specs may not be so high.

Those unable to run Vista have until 2011 to upgrade, when support ends for XP.